There are known a fluid reservoir for containing fluid, such as chemicals for dental treatment, and dental apparatus in which such a fluid reservoir is installed for supplying chemicals to a dental handpiece. Such a fluid reservoir and dental apparatus are disclosed in JP-2002-320628-A. The fluid reservoir disclosed in this publication has a connector piece to be fitted in a reception member of the dental apparatus, and the connector piece is provided with two one-way check valves. One of the one-way check valves has a valve ball arranged over a discharge opening of the fluid reservoir. The valve ball is biased by a spring toward a valve seat to close the discharge opening. The other of the one-way check valves also has a valve ball biased by a spring to close an aeration opening. When the fluid is drawn out of the fluid reservoir to produce negative pressure inside the reservoir, the valve ball is pushed up against the biasing force of the spring, and air is taken into the reservoir through a clearance formed between the valve ball and the valve seat to balance the internal pressure of the reservoir.
In the apparatus of JP-2002-320628-A, upon replacing the fluid reservoir, negative pressure may be produced inside the fluid reservoir. Since the fluid reservoir is provided with the aeration one-way check valve, the fluid in the reservoir may flow out through the aeration opening of the valve under the action of the negative pressure. In addition, providing two valves for one fluid reservoir disadvantageously complicates the production process since a larger number of parts are involved. Further, when the interior of the fluid reservoir is washed for repeated use, the two valves provided thereon should be opened and closed for cleaning, which is complicated and bothersome.